This application will bring together the expertise of different investigators and incooperate state of the art platform technologies with the goal to optimize monoclonal antibodies (mAb) to Staphylococcal enterotoxin B (SEE) for human use. Beyond the immediate benefit of yielding a novel therapeutic reagent, this work will investigate several hypotheses that pertain to toxin-neutralization and clearance. The underlying working hypothesis of our proposal is that high affinity anti-SEB mAbs are best suited for therapeutic use because low amounts of mAb will be sufficient to successfully compete with already bound SEB. We will investigate if human mAbs differ and are superior in their ability to neutralize toxin, In addition we propose that targeted engineering of the C-terminal with effects on FcR binding will change toxin clearance in vivo. In the past funding period 11 mAbs to SEB have been subcloned, characterized and tested in murine animal model for SEB induced shock. A highly sensitive capture ELISA was developed that will allow us in proposed experiments to measure SEB toxin in serum of intoxicated mice. In addition the prevalance of SEB producing S. aureus strains has been established and identified important sequence variabilities in different S. aureus strains which will be taken into consideration. Three lgG1 candidate mAbs have been selected for targeted Ab engineering. They recognize epitopes in the C-terminal part of the protein, which is also the predominant epitope recognized by human B-cells. Protection was documented in animal models and human T-cell stimulation assays. In addition heavy and light chain variable regions of the mAbs were cloned. In Aim one we propose to optimize these mAbs by affinity maturation in collaboration with Dr. Scharff. In Aim 2 we propose to generate new human SEB apecific mAbs one involving a genetically modified mouse that expresses the human variable region and the other one we will use Drs. Ahmed/Wilson's technique to directly clone the variable region from patients with primary S. aureus infection. Finally in aim 3 we will engineer the FC binding portion of the mAbs in collaboration with Dr. Ravetch and test the intriguing hypothesis that combination of mAbs enhances neutralization and clearance.